The objective of this work is to characterize the properties and regulation of specialized plasma membrane transport systems in the MDCK kidney epithelial cell line. Methodology will be developed to characterize transepithelial transport of labeled solutes by intact cell monolayers grown on porous supports using a two-chamber flow-through apparatus. Also, methods for purification and characterization of plasma membrane vesicles from the apical and basolateral cell surfaces respectively of MDCK cells grown in culture will be developed as an approach to study transport mechanisms in a cell-free system derived from a clonal cell culture exhibiting plasma membrane polarization.